$ E = \left[\begin{array}{rrr}1 & 1 & 1 \\ 2 & 1 & 0 \\ 2 & 2 & 0\end{array}\right]$ What is $ E^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}0 & 1 & -\frac{1}{2} \\ 0 & -1 & 1 \\ 1 & 0 & -\frac{1}{2}\end{array}\right]$